Treatment for the frogs to me is uncharted territory for diseases. Probably not Ich, I was told only fish are hosts for that.
See if it wipes off with a cotton swab, or you could tie a cotton swab on a chop stick if you can't quite get that close.
Check water parameters and do a pwc
if not in the safe zone and maybe vac out any crud in the substrate especially feeding areas and low flow corners which can accumulate "stuff".